Typical of the brake or clutch units with which the invention is concerned are units in which engagement is effected between one or more metal brake discs and one or more discs of friction material of a disc pack, by axial movement, to effect a braking action between members carrying the respective discs, or to couple them rotationally together. In such units, the or each disc of frictional material in particular experiences considerable wear and the axial movement needed to effect braking or clutch engagement correspondingly increases progressively, as the wear increases. Brake or clutch operation is consequently delayed and this can be a serious disadvantage where prompt application is required. Such wear can be accommodated by replacement of the friction discs, or by manual adjustment of the components of the unit. In either event, the time of service personnel is employed and the unit is out of use for a substantial period.
The present invention accordingly has as an object the provision of a brake or clutch unit in which disc pack wear is compensated for automatically, that is, in response to its occurrence.